Construction of sound record film



DMn 9, 1941. w. L. WOOLF 2,265,960

CONSTRUCTION OF SOUND RECORD FILM Filed April 26, 1940 VBY I ATTORNEYPatented Dec. 9, 1941 UNITED STATES PATENT OFFICE CONSTRUCTION or soUNnaaoonn mM william L. woon, Bayside, N. Y. Application April ze, 1940,serial No. 331,701 2 Claims. (ol. 274-43) l This invention' relates to anlm upon which sound may be recorded and from which sound may bereproduced. It relates particularly to a film which is perforated nearits edges and in which the two ends are joined together so that the filmis a continuous one.

The primary object of the invention is to provide a film of thischaracter in which the number of tracks and the space between theperforations and edges of the film bear such relation to each other thata film of standard width will stand the greatest average amount of use.

In a standard nlm of 35 mm. in width, it is entirely practical toproduce sound tracks with a stylus, which tracks may be so closetogether that 120 of them to the inch may be recorded side by sidewithout danger of one sound track interfering with another. Such tracksin a celluloid iilm are more permanent than the lm itself. That is tosay the total playings the track will stand without wearing out thetrack beds, is greater than the number of times the film will go throughthe machine without wearing out or breaking.

In a machine using a continuous film such as here contemplated, theentire film goes over the various feed rolls and sprocket each time onesound track is recorded or reproduced. As the number of tracksmultiplies, the amount of wear on the film increases, hence the factorof wear becomes important in determining the width of film which willallow the greatest average amount of use.

If a wide film is used, a great many tracks are available, but the lmwill wear out before all of the tracks are utilized. If, on the'otherhand, the film is made quite narrow, there is a loss of economy in theutilizable space because whether a film is wide or narrow, there mustnecessarily be two outer marginal edges, two rows of perforations andtwo margins within the perforations whether a few tracks are used ormany.

In the standard film such as employed in the moving picture industry,the point of greatest weakness lies between the outer edges of the filmand the corners of the perforations. The first breaks to occur when aillm of this character is put to a break-down test, extend across thenarrow strip between the perforations and the outer edge.

A feature of the present invention relates to a. film constructionwherein that portion of the iilm between the outer edges of theperforations and the edges of the film is made wider than the sameportions in a standard nlm of standard width.

In the drawing, Figure 1, is a small portion of a standard 35mm. film;and

Figure 2 is a similar view of a film constructed in accordance with thepresent invention.

In a standard 35 mm. motion picture film, the distance between the edgeof the perforations and the edge of the film is .0795.

In the lln of the present invention, shown in Figure 2, this width isincreased to .114"; the difference being .035 or 44%. By reenforcing theedge of the film by the above amount and with standard perforations,such a nlm can with safety be relied upon to run through the recordingmachine 3500 times.

The number of sound tracks which it is most advantageous to record on agiven piece of iilm will of course depend upon the average number oftimes which each sound track is played and this of course will dependupon the nature of the recordings, the taste of the user and the natuzeof the use of the recordings, whether for pleasure, information oreducation, it being apparent that it is futile to put more tracks on thelm than can be successfully utilized before the film breaks down.

The average of a number of studies of this subject indicates that thenumber of desired playings per track is 36.08. Therefore, if the totalnumber of playings which the iilm will stand is equal to 3500 and theaverage number of times each trackn is played is 36.08 then the numberof tracks that a 35 mm. film may conveniently accommodate is equal to97.`

Therefore by increasing the width of that portion of the film betweenthe outer edge of its perforations and the edges of the film by 44% asstated above, the film will wear as long as the average number ofplayings of its 97 sound tracks, is subjected, and without unnecessarywaste of available playing space. The standard perforations are .110"wide. Since there are two sets of perforations, one on each edge of thelm, the total space occupied by the perforations is .220. As clearlyindicated in Figure 2, the width between the perforations and the edgeof the film is .114", thus leaving a space available for recordationsequal to .929. Of this space 97 tracks at 120 tracks to the inch occupy96 1A20+-004 inch=.804 inch; .004" being the width of a single track.Allowing a margin of .0625" on either side of the recorded area, thetotal width of .929" is utilized.

It will thus be seen that the standard 35 mm.

2 aacaeeo film is capable of operating at maximum usefulness byincreasing the width of each of its outer margins by .035, thusdiminishing the distance between perforations by twice this amount andleaving room for 97 tracks at 120 tracks per inch. The figure 97 alsolends itself to convenient counting of the tracks since the largestnumber that can be indicated on a two-place counter is 99.

In the foregoing specication reference has been made to a standard iim.By such iilm is meant a lm of 35 mm. in width with the size and spacingof the perforations as indicated in i0 width (35 mm.), the distance`between the inner edges of its perforations being of the order of .929.

WHLIAM L. WOOLF.

